Cytogenetic studies and the occurrence of triploidy in the wild potato species Solanum commersonii Dun.

Summary The South American wild potato species Solanum commersonii Dun. exists as two subspecies, subsp. commersonii and subsp. malmeanum (Bitter) Hawkes and Hjerting, and as both diploid and triploid cytotypes. The two subspecies were completely cross fertile but there were reciprocal differences in the number of seeds set per berry and the mean seed weight. Crosses between diploids and colchicine-induced autotetraploids yielded only a few seeds per berry, but 16 of the 18 germinated seeds were triploid or nearly so. Such a high proportion of triploids is unusual for such crosses in potatoes. Some triploids has a high percentage of stainable pollen. The origin of naturally occurring triploids is discussed in the context of 2n gametes, a triploid block, and endosperm balance numbers.     

Incompatible pollen tube growth and protein composition in styles of Japanese pear following high temperature treatments

Summary Immersing the excised-prepollinated styles of self-incompatible Japanese pear, Pyrus serotina Rehd., into distilled water at 45°C for 1.5–2.5 min promoted the growth of self-pollen tubes; both the number of styles penetrating the pollen tubes through styles to cut ends and of pollen tubes protruding from cut ends were increased. The subsequent growth of the protruded pollen tubes on agar media was also enhanced by the treatments. Treatments at 40°C did not promote the growth of self-pollen tubes and those at 50°C led the styles to necrosis. In the stylar proteins analyzed by isoelectricfocusing polyacrylamide gel electrophoresis, several changes in banding pattern were found following the heat treatment; one of the bands was a glycoprotein that increases in quantity in developing styles as self-incompatibility of the style becomes stronger (Hiratsuka et al., 1986). This protein band was stained more weakly by Coomassie Brilliant Blue-G250 dye. Antigenic substances in the styles examined by immunodiffusion seemed not to be denatured by high temperature treatments.Abbreviations IEF-PAGE isoelectricfocusing polyacrylamide gel electrophoresis - CBB Coomassie Brilliant Blue     

Inter-varietal pollen tube growth and ovule penetration in the avocado

Summary Results are presented showing number of pollen tubes in the pistil, and ovule penetrations in crosses involving the avocado varieties Edranol, Ryan, Hass, Reed, Talbot, Jalna, Fuerte, Bacon and Sharwil. Between 5% and 100% of the ovules in each cross were penetrated by a pollen tube. The female parent exerted more control than the male on numbers of tubes and ovule penetrations and the results for type A varieties were more consistent than those for type B varieties. Penetration of an ovule by two tubes was observed in all varieties except Reed and Fuerte and penetration of an ovule by three tubes was observed in the variety Edranol only. With the possible exception of the variety Bacon as female parent there was no difference between pollination with pollen from type A or B varieties.     

Induction of novel organelle DNA variation and transfer of resistance to frost and Verticillium wilt in Solanum tuberosum through somatic hybridization with 1EBN S. commersonii

Somatic hybridization can be used to induce genetic variability in plastidial and mitochondrial genomes, and transfer multiple uncloned genes across sexual barriers. Somatic hybrids were produced between a dihaploid clone of the common potato, S. tuberosum subsp. tuberosum, and the wild sexually incongruent diploid species S. commersonii. Fusion products were selected on the basis of callus growth and regeneration in vitro. Genome composition of putative somatic hybrids was determined by flow cytometric analysis of nuclear DNA content, RAPD analysis, and Southern analysis with probes specific to organellar DNA. All regenerated fusion products proved to be hybrids based on RAPD analysis. Seventy per cent of somatic hybrids were (near) tetraploids, 22% (near) hexaploids and 8%(near) octoploids. A high correlation was found between the nuclear DNA content determined by flow cytometry and the number of chloroplasts in stomata guard cell pairs. Somatic hybrids inherited the parental plastids in a random manner. On the contrary, they preferentially inherited the mitochondrial DNA fragments of S. tuberosum. The majority of them had a rearranged mitochondrial genome with fragments from both parents. Hybrids were highly vigorous and morphologically more similar to the cultivated than to the wild parent, produced tubers on long stolons under long photoperiod conditions, showed a high degree of flowering, but did not produce pollen. In addition, somatic hybrids were generally more resistant to frost and Verticillium wilt than the cultivated parent, indicating the introgression of relevant resistance genes from the wild species into the genetic background of S. tuberosum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of different pollen viability assays to evaluate pollen fertility of potato dihaploids

Summary The main obstacle in breeding potato (Solanum tuberosum L.) dihaploids is the severe limitation of male fertility. To determine pollen viability assays that correlate well to fertility in crosses, results of five different pollen viability assays were compared by correlation analysis with fruit and seed set characters in test crosses, and to pollen tube growth in situ (PL-test). The methods used were: staining the pollen cells with carmino acetic acid (CAA-test); in vitro pollen germination (PG-test); and detection of pollen staining rates after incubation with fluoresceine diacetate (FDA-test), 2-3-5-triphenyle tetrazolium chloride (TTC-test), and 5-bromo-4-chloro-3-indolyle--galactoside (X-Gal-test).The results of test crosses and pollen tube growth in situ correlated with the results of all other assays with the following ranking, from highest to lowest: enzyme activity assays (X-Gal-test, FDA-test, TTC-test), in vitro pollen germination (PG-test), and pollen staining by CAA. The newly developed X-Gal-test for monitoring -galactosidase activity showed the least variation of all assays investigated. Thus, this highly reproducible simple procedure is recommended for male fertility screening.Abbreviations B/F Berries obtained per 100 flowers - CAA Carmino acetic acid - FDA Fluoresceine diacetate - PG Pollen germination rate in vitro - PL Pollen tube growth in situ - S/B Seeds per berry - S/F Seeds per pollinated flower - TTC 2-3-5-triphenyle tetrazolium chloride - X-Gal 5-bromo-4-chloro-3-indolyle--galactoside     

Diversity in the wild potato species Solanum chacoense Bitt.

Summary The morphological and isozyme variation was studied in 22 accessions of Solanum chacoense from Paraguay and Argentina. Clear geographic groups were identified through the use of multivariate analyses. S. chacoense from mountain sites in Argentina could be readily distinguished from plains forms from Paraguay, on the basis of several correlated morphological characters. Three isozyme systems, namely phosphoglucose isomerase (PGI), glutamate-oxaloacetate transaminase (GOT) and peroxidase (PRX) were studied using starch gel electrophoresis. The banding patterns indicated that for each isozyme there were several loci, which were polymorphic. A genetic interpretation of one of the PGI loci was made, and indices of genetic diversity and genetic identity calculated. Principal components analysis, cluster analysis and genetic diversity indicated a close relationship between the geographical groups. These results are discussed in the context of in situ genetic conservation.     

Differential pollen tube growth in inbred self-compatible almond genotypes

Pistil and pollen behavior during self- and cross-pollinations in 10 inbred almond seedlings with self-compatible genotypes and self-incompatible phenotypes were studied. Pollen from these inbred seedlings was examined for the pollen tube growth in self and non-self styles, while pistils from these seedlings were tested for their ability to support self and non-self pollen tube growth. Pistils and pollen of inbred genotypes were compatible with unrelated genotypes but the pistils were unable to support the growth of related pollen, which showed a slower tube growth rate. This may be a consequence of inbreeding, resulting in a silenced self-compatibility or cryptic self-incompatibility in some genetically self-compatible genotypes. This reaction would be a mechanism favoring crossing with unrelated genotypes and reducing inbreeding in future generations.     

Pollen and pollination experiments. V. An empirical basis for a mentor pollen effect observed on the growth of incompatible pollen tubes in pear

Summary The self-incompatible pear cultivar Doyenne du Comice was selfed with the aid of the mentor pollen technique (self pollen mixed 1:1 with compatible pollen) and the pioneer pollen method (compatible pollen applied 14 h in advance of the self pollen). Observations on tube growth in the style showed that inviable methylated pollen was ineffective either as mentor or pioncer pollen, having no effect on the performance of the self pollen which stopped growing at about one quarter of the style from the stigma. Calculations made on the basis of the obtained data indicated that the viable untreated or irradiated pioneer and mentor pollen, the former somewhat better than the latter, aided the self pollen tubes to reach the base of the style.     

Chloroplast DNA variation in the wild potato species, Solanum acaule and S. albicans

The chloroplast DNA of Solanum acaule (109 accessions) and S. albicans (9 accessions) was investigated by restriction endonuclease analysis. Unexpectedly, all the accessions analyzed had C type chloroplast DNA in common. This suggested that S. acaule originated from a species with C type chloroplast DNA. DraI restriction digestion revealed further differentiation of C type chloroplast DNA into 8 types. The DraI polymorphism indicated the province of Salta in Argentina and the nearby regions to be a center of diversity for S. acaule. Surprisingly, S. albicans as well as S. acaule both ssp. acaule and ssp. punae, from Peru were virtually indistinguishable, although by morphology and/or cytology all three taxa are easily distinguished. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors affecting haploid production in wheat using the Hordeum bulbosum system. 1. Genotypic and environmental effects on pollen grain germination,pollen tube growth and the frequency of fertilization

Summary A quantitative examination of pollen grain germination and pollen tube growth within the overy wall was made in selected wheat × tetraploid H. bulbosum hybridizations, to investigate the effect of the wheat and the H. bulbosum genotype on these characters. As expected, variation at the known crossability loci had no effect on pollen grain germination. The frequency of pollen tube penetration of the ovary wall was, however, severely reduced when the dominant alleles were present. Pollen tube penetration was nevertheless observed in 3 of the 110 ovaries examined of the non-crossable cultivar Highbury. The H. bulbosum genotype had a much smaller effect on these characters, but significant differences between the clones were observed in the numbers of pollen tubes initially penetrating the ovary wall. Although two H. bulbosum genotypes showed no significant differences in the number of ovaries with pollen tubes at the base of the ovule, significant differences in the frequency of fertilization were observed. The possible cause of this discrepancy is discussed.The frequency of fertilization in crossable wheat × H. bulbosum hybridizations was improved by the application of gibberellic acid within 10 minutes of pollination, and reduced by an increase in the ambient temperature from 20°C to 26°C. Fertilization following the pollination of non-crossable wheat genotypes was not affected by either of these factors.     

The site of action of the crossability genes (Kr 1, Kr 2) between Triticum and Secale. I. Pollen germination,pollen tube growth,and number of pollen tubes

Summary Seven genotypes of common wheat (Triticum aestivum L.) were crossed with rye (Secale cereale L.) in order to find the site or sites of action of the crossability genes, Kr ₁ and Kr ₂, of wheat. The data obtained, by fluorescence microscopy, were compared to the controls (wheat x wheat). The results indicate that the crossability genes have little effect on pollen germination and on the time taken for the pollen tubes to reach the microphyle, irrespective of their crossabilities with rye. The number of pollen tubes reaching the microphyle is, however, affected by the Kr-genes, as high crossable genotypes have more pollen tubes than the low crossable ones. There was a high correlation between the mean number of pollen tubes at the micropyle with seed set, which also reflects the crossability. The Kr-genes seem to manifest themselves in the retardation and inhibition of pollen tube growth between the style base and the top of the embryo sac, where the effect is most distinct in the low crossable genotypes.     

The crossing of common wheat (Triticum aestivum L.) with cultivated rye (Secale cereale L.). I. crossability,pollen grain germination and pollen tube growth

Summary The crossing of common wheat (Triticum aestivum L.) with rye (Secale cereale L.), and especially the action of the crossability genes of wheat, was studied using the readily crossable wheat cv Chinese Spring (genotype kr ₁ kr ₁ kr ₂ kr ₂ >), the poorly crossable wheat cv Hope (genotype Kr ₁ Kr ₁ Kr ₂ Kr ₂ ), as well as the disomic substitution line of chromosome 5B of Hope into Chinese Spring (CS/Hope 5B, genotype Kr ₁ Kr ₁ kr ₂ kr ₂ ). By comparing crossability and actual fertilization, the poor crossability with rye of both cv Hope and the CS/Hope 5B substitution line was shown to result from absence of fertilization. Studies of pollen grain germination and pollen tube growth showed that the dominant alleles of the crossability genes manifested themselves through retardation and eventually inhibition of pollen tube growth at the style base and in the ovary wall. In Hope the growth of all pollen tubes was inhibited, whereas in CS/Hope 5B rarely fertilization was achieved. The recessive alleles of the crossability genes do not seem to have an influence on the growth of rye pollen tubes in wheat pistils.     

Breeding of the cultivated potato species Solanum x juzepczukii Buk. and Solanum x curtilobum Juz. etBuk.

Summary This study investigated the possibility of recombining anew the genomes of the wild and cultivated progenitors of triploid S. juzepczukii and pentaploid S. curtilobum by following the known evolutionary pathway of these two species. Before starting the actual breeding work, the natural variation of S. juzepczukii, S. curtilobum and their wild progenitor S. acaule was studied from the point of view of morphology, quantitative and qualitative tuber glycoalkaloid content and frost resistance. The morphological study was supplemented by a study of the soluble tuber proteins employing polyacrylamide slab-electrophoresis. From 137 accession of S. juzepczukii only 19 morphotypes were identified, 18 of which were also different in their protein spectra. The only red-tubered S. juzepczukii revealed a protein spectrum identical to that of the largest white-tubered group. On phylogenetic grounds, the occurrence of a red-tubered S. juzepczukii cannot be explained. It is concluded that this red clone is a somatic mutant for tuber colour which arose from a whitetubered clone. S. curtilobum was restricted in its variation to just two morphotypes differing only in tuber colour which are, however, identical chemotypes. This would be the case if one of the clones was a somatic mutant for tuber colour from the other one. The glycoalkaloids -solanine, -chaconine, tomatine, demissine and - and -solamarine are shown to be useful taxonomic characters which confirm earlier hypotheses on the origin of S. juzepczukii and S. curtilobum. Laboratory tests showed the two cultivated species to be resistant to about –3°C whereas S. acaule is resistant to temperatures sometimes below–5°C. The diploid progenitor of S. juzepczukii, S. stenotomum, also has forms resistant to –3°C. The results of this study demonstrate that the proposed breeding scheme is possible.     

The progamic phase in Cichorium intybus L. Pollen tube growth in the style,incompatibility reaction and gametophytic competition

Summary Pollen germination and tube growth were studied following compatible, incompatible and pseudo-compatible pollinations in chicory. Pollen germination begins 3 minutes after compatible pollinations. The earliest pollen tubes reach the ovary 17 minutes later. Many of the later germinating pollen tubes are arrested and burst at the stigma papillae. In the transmitting tissue inhibitional effects due to negative interactions between pollen tubes are frequently observed. Complete self-incompatibility results in total inhibition of germination. In case of pseudo-self-compatibility, some pollen germinate but germination and stigma penetration are delayed and often result in pollen bursting. There is no self-incompatibility reaction in the transmitting tract but if the pollen tubes reaching this tissue are relatively numerous, negative interactions between them occur as after compatible pollinations. An hypothesis is presented which attributes the negative interactions between pollen tubes to the diffusion of a substance from the growing pollen tubes. This substance would also provoke pollen bursting on the stigma.     

Estimating pollen fertility in Solanum species and haploids

Summary Three staining methods (acetocarmine, fuchsin and oxidation of benzidine) and germination in vitro and in vivo were applied to estimate pollen fertility in Solanum species and dihaploids. Pollen was divided into six classes based on shape and contents of the grains. With acetocarmine, fuchsin, peroxidase and germination in vitro 4, 3, 2 and 1 classes, respectively, are supposed to be included in the percentage of good pollen as measured by these methods. This percentage therefore, in more than 96% of the cases studied, shows a decrease in the order indicated. Neither aging of pollen at room conditions nor collecting pollen from flowers on 1–9 days after anthesis does influence the percentage of good pollen with acetocarmine and fuchsin, whereas this percentage drops sharply to zero with peroxidase and germination in vitro. The latter two methods apparently measure as good pollen only the grains with living cytoplasm. When pollen is collected at three successive dates from the same flowers the percentage of good pollen drops sharply with all methods used. There is a relation between quantity of pollen per flower and pollen quality (% good), low-quantity pollen containing significantly lower percentages of good pollen than medium- and high-quantity pollen. The latter two are not significantly different in this respect.From calculations of correlation coefficients it is concluded that only germination of pollen in vitro is significantly correlated with berry and seed set and thus gives a reliable estimate of male fertility. This does not hold true for the two staining methods without due reserve. The peroxidase method is not useful for the Solanum material studied.After standardized pollination the average number of haploid pollen grains on diploid stigmata was found to be 1625±127, that of diploid pollen on tetraploid stigmata 2863±98.A. W. B. Janssen 1975.     

Interspecific hybridization in Cucumis L. II. The crossability of species,an investigation of in vivo pollen tube growth and seed set

Summary The crossability of 12 Cucumis species of African and Asiatic origin was studied in a diallel cross, in order to find ways to realise the cross between the common cucumber (C. sativus L.) and its wild relatives which carry resistances against diseases and pests.Self-pollinations and cross-pollinations within species gave normal pollen tube growth and seet set. The different accessions within a species, as a rule reacted alike in interspecific crosses. In crosses between African species different crossing patterns were found, viz. bilateral congruity, bilateral incongruity and unilateral incongruity. Within C. sativus all accessions intercrossed freely, except one, which displayed unilateral incongruity.Good seed was harvested from several crosses and in some cases embryo culture was needed for further development of seeds. No good seeds were obtained from any cross between a species of the African group and C. sativus L.     

Effects of high temperatures on mature pollen grains in wild and cultivated maize accessions

Summary The effects of high temperature on mature pollen of various maize lines were investigated. Genotypic differences in pollen reaction to high temperature were revealed. Pollen grains resistant to high temperature (35°C, 26°C) were characterized by higher germination capacity and better ability to develop normal pollen tubes. The studies are of interest to evaluate reproductive system tolerance and conduct gamete selection at the mature pollen grain stage in maize.     

Low temperature tolerance of biomass and pollen germination in potato clones of Andean and European origin

Summary The temperature-related performances of six tetraploid potato clones, two Andean, three European, and one hybrid, were compared by cultivating them in growth chambers under one of two temperature regimes: 10°C day/4°C night or 20°C day/10°C night. Preformance was measured in terms of biomass production and pollen germinability.For dry matter yield at second harvest, the temperature-related performance ratios (performance at 10°C/4°C divided by performance at 20°/10°C) were highest for the Andean clones, intermediate for the Andean/European hybrid clone 201₅×S₁₂, and lowest for the European cultivars. The ability of the European cultivars to maintain their normal rates (i.e. rates at 20/10°C) of biomass production when cultivated at low temperatures varied greatly, with clone S₃ performing most poorly at 10/4°C.For pollen germinability in vitro, performance ratios were highest for the hybrid clone 201₅×S₁₂ and lowest for the European clones.The high tuber yield of hybrid 201₅×S₁₂ at 10/4°C can be attributed to its low-temperature tolerance and it being daylength neutral.     

In vitro pollen germination and tube growth of tomato (Lycopersicon esculentum Mill.) and its relation with plant growth

Summary In vitro pollen germination at 10°C, 14°C and 22°C of four groups of two pure line tomato varieties was compared with their plant growth at 19°C D/10°C N under controlled environmental conditions. Generally, pollen germination was slow at 10°C but after 6 h the percentage of germination was similar to that at 22°C. Maximum germination was obtained at 14°C already after 4 h. The longest pollen tubes occurred at 22°C. The two varieties within each group differed significantly from each other for percentage of pollen germination. For one group, this difference was greater at 10°C than at 22°C. The varieties in two groups also differed significantly for pollen tube growth. These differences in pollen tube growth rate were greater at 22°C than at 10°C. There was no clear relationship between pollen germination, pollen tube growth and plant growth in any of the four pairs of varieties. The results are discussed with regard to the possibility of pollen selection at low temperature in order to improve the efficiency of breeding for growth at low temperature.     

Overcoming the self-incompatibility of Raphanus sativus by application of plant hormones,amino acids and vitamines,and by temperature treatment of pollen

Summary Overcoming self-incompatibility by application of three kinds of plant hormones, sucrose, 3 kinds of amino acids and 2 kinds of vitamines was tested in cvs. Honbashi-taibyo Minowase (H-Mino) and Minowase (Mino) of Raphanus sativus. Effects differed between the cultivars. In H-Mino, BA (100 mg/l) and glutamic acid, folic acid and nicotinic acid (500 mg/l) resulted in higher fruit set and higher number of seeds per pollinated flower. In Mino, BA and NAA (100 mg/l) and glutamic acid and glycine (500 mg/l) induced a high number of seeds per pollinated flower. These chemicals, however, induced parthenocarpic fruit set, especially GA3. From the observation of pollen on stigmas washed with glutamic acid, it appeared that the pollen-tube penetrated into a papilla cell after 1 hour and openings of papillae and detached pollen grains and tubes were found after 2 hours as the result of successful pollentube penetration of papillae. Pollen was heated at 50°C for 30, 45 or 60 minutes, at 60°C for 15, 30 or 45 minutes and at 70°C for 10, 20 or 30 minutes prior to self-pollination. In H-Mino, 60 and 70°C were effective, and expecially 60°C for 15 or 30 minutes resulted a higher percentage fruit set and more seeds per fruit. In Mino, although 50–70°C were effective, the mean number of seeds per pollinated flower was lower than in H-Mino.